Tough new restrictions to keep possible abusers away from children will "inevitably" sweep up people who will not abuse any children, the Ministry of Justice says.
In advice to the Government, the ministry estimates that only about half the people subjected to child harm prevention orders would have gone on to offend without the order.
Others would not have abused children and would suffer a "curtailment of fundamental freedoms without any corresponding benefits".
"The inherent uncertainty of risk prediction means that orders would inevitably be imposed on people who would not have committed child abuse in the absence of the order."
The proposed orders, which were announced by the Government last month, can ban people from contact with any children or from visiting places frequented by children, such as swimming pools. They can be imposed even if the person has no convictions and last up to to 10 years.
The ministry acknowledged the orders would be seen by "many people as punitive and ... an infringement of fundamental rights".
The comments have been seized upon by civil liberty experts, who claim the orders will erode the traditional presumption of innocence.
"We always assume it will happen to someone else, but who would volunteer to live under one of these orders, even to protect kids?," Otago University law professor Andrew Geddis said.
Social Development Minister Paula Bennett said a great deal of effort had been put into minimising the chance that the wrong people could be placed under such orders. The process would be controlled through the courts, with only a few public service heads able to apply for an order.
"I can't deny they may be some people [under the orders] that won't offend against children," she said.
"But at the end of the day, we have a chance to stop children being harmed and seriously injured and I think we have got that balance right."
The ministry estimates about 200 people will be subjected to an order over time, but only 100 "would have, in fact, offended without the order".
The ministry refused to comment on its advice, but a spokeswoman for Ms Bennett's office said it did not mean the other 100 would not offend, only that they were unlikely to be convicted.
In its advice, the ministry recommends the orders be adopted despite the risks.
"Benefits in providing protection for vulnerable children who cannot take steps to protect themselves outweigh the fiscal and other costs."
The protection orders are part of a wider Government's strategy to curb the appalling child abuse record, with a bill introduced in Parliament last week.
More than 50 children have died in the past five years because of extreme abuse and Child, Youth and Family reported 21,000 confirmed cases of child abuse and neglect in 2009 alone.
Other proposed changes include stricter vetting of tens of thousands of government employees, removing children from abusive parents, and stronger requirements from state sector leaders to curb child abuse.
But while many measures have received broad support, critics say the orders set a dangerous precedent.
"People will be treated as pariahs and as guilty without ever being found guilty," Otago University law professor Mark Henaghan said. "That can destroy people."
Colin Gavaghan, director at the NZ Law Foundation centre for emerging technologies at Otago, said the orders were part of New Zealand move towards a "pre-crime" society, with people condemned on probability rather than proof.
- The Dominion Post